There are many reasons why we might want to compare and contrast layers within our projects. These include:
Detecting change between multiple dates
Assessing geo-location accuracy and spatial offset between datasets
Evaluating the effect of spatial resolution differences between layers
Visualising how a vector layer compares with underlying image data
For a super quick visual assessment...
Select the uppermost layer or feature that you want to compare (vector or raster), and the compare tool will activate.
Click on the compare tool
Use your mouse to swipe left and right to reveal what's below.
To disable the compare tool, choose another tool (e.g. the pan) instead. Using a keyboard shortcut is particularly effective (e.g. click 'h' to pan).
You can continue to zoom in and out while you are comparing by using the wheel on your mouse.
Activate pan while using the compare tool by holding down the shift key and then clicking and dragging as per usual. Release the spacebar to return to the swiping functionality.
You can compare multiple layers at once by holding shift or control while selecting them in the table of contents. This works particularly well if you have multiple adjacent datasets.
You can activate the compare tool by selecting individual features within a vector layer - you don't need to swipe the entire layer.
You can activate the compare tool by selecting orthomosaic, DSM, or DTM - you don't need to swipe the entire layer. This means that you can compare the orthomosaic to its DSM or DTM, or compare the DSM to the DTM.
Reorder your vector layers and raster datasets by clicking and dragging them to a new position in the Table of Contents if you want to compare layers in a different order.
Make sure that the layer / dataset you are swiping isn't below something else, otherwise you won't see the effect
Make sure that the layer / dataset you are swiping is visible, and the opacity is not set to 0.
The compare tool will only activate when a feature, layer, or dataset is selected.